Introduction of antigens by the oral route in adult animals induces a state of antigen-specific non-responsiveness. The mechanism by which this non-responsiveness is mediated is not well understood, however, increasing evidence suggests that the state of non-responsiveness is mediated by clonal anergy and/or by the induction of antigen-specific regulatory T cells. In murine models of experimental allergic encephalomyelitis, oral administration of myelin basic protein (MBP) in adults induces antigen- specific T cells that mediate their effector functions by producing suppressive cytokines. The repertoire of T cells induced following oral administration of an antigen has not been defined. Furthermore, the antigenic epitopes (helper, anergizing or regulatory) that are generated following oral feeding of an antigen, their MHC binding characteristics and the mechanism by which they mediate protection have not been defined. In contrast to oral tolerization in adults, our preliminary results suggest that oral feeding of an antigen in neonates results in immunological priming leading to enhanced immune responses to the antigen as an adult. However, the cellular and molecular mechanisms responsible for such contradictory effects are also not clear. The primary goal of this portion of the program project is to define the antigenic epitopes that are generated by antigen processing and presentation via the gut and study the T cell responses to these epitopes in adults and in neonates. We propose to: 1) identify epitopes and define the repertoire of T cells induced following oral administration of MBP in adult mice. This will be accomplished by generating T cell clones and hybridomas from orally tolerized mice which will be used as tools to define: A) tolerogenic epitopes; B) diversity of the T cell repertoire including T cell receptor usage; C) MHC requirement of these cells and D) to identify gut associated antigen presenting cells 2) study the effect of oral administration of MBP in neonates on the development and selection of helper vs. regulatory T cell repertoire. Neonates will be fed with the antigen and then tested as adults to determine whether oral administration of antigen specifically A) deletes antigen-specific regulatory cells or b) preferentially selects and expands the antigen-reactive helper/encephalitogenic T cell repertoire. The mechanisms of neonatal priming will be further studied in the MBP-specific T cell receptor transgenic mice. Furthermore, the results on the epitopes and T cell repertoire generated by oral feeding of the neonates will be directly compared with adults fed the same antigen. These studies will provide broad basic information regarding the mechanism by which oral administration of antigen mediates non-responsiveness in the adult and will provide better understanding of the cells and epitopes that are involved in mediating oral tolerance. The studies on immunological priming mediated by orally administered antigen in neonates may also provide an insight into the cellular and immunological mechanisms responsible for food allergies.